Tests for #238. Assert analogWrite not called with NaN when calling pulse for the first time
Fixes #238. Ensure the current value is at least the number 0 (it may be null or 0)

Signed-off-by: Rick Waldron <waldron.rick@gmail.com>
Adds "analog" accessor property to Sensor

Signed-off-by: Rick Waldron <waldron.rick@gmail.com>
IR.Distance class

- Inherits from Sensor
- Requires a device/model id for initialization.

Signed-off-by: Rick Waldron <waldron.rick@gmail.com>